Method of transmitting transmission data from sensor controller to pen, and pen

ABSTRACT

[Object] To allow a pen to properly receive an uplink signal even if there is dullness in a waveform of the uplink signal. [Solution] Provided is an invention of a method of transmitting transmission data from a sensor controller  31  that detects a pen  2  to a pen through a sensor electrode group  30 . The pen  2  includes a pen tip electrode arranged near a pen tip, an analog circuit that detects edges of a signal led to the pen tip electrode, and a digital circuit that performs a correlation operation of an output signal of the analog circuit and known patterns to detect transmission data. The sensor controller  31  generates a pulse signal representing the transmission data and transmits the pulse signal, by using a main signal and a sub signal of the pulse signal so as to enhance the edges, thereby transmitting the transmission data through the sensor electrode group.

TECHNICAL FIELD

The present invention relates to a method of transmitting transmissiondata from a sensor controller to a pen, and a pen.

BACKGROUND ART

A position detection system is known that includes an active stylus(hereinafter, referred to as a “pen”) that is a position indicator withinternal power supply, and a position detection apparatus including atouch surface. In this type of position detection system, signals aretransmitted and received between the position detection apparatus andthe pen through a sensor electrode group arranged just below the touchsurface. The signals (hereinafter, referred to as “uplink signals”)transmitted from the position detection apparatus to the pen play a roleof synchronizing the pen with the position detection apparatus and playa role of transmitting various commands to the pen. On the other hand,the signals (hereinafter, referred to as “downlink signals”) transmittedfrom the pen to the position detection apparatus play a role of causingthe position detection apparatus to detect the position of the pen andplay a role of transmitting data requested by commands to the positiondetection apparatus.

Examples of the position detection system are disclosed in PatentDocument 1 and Non Patent Document 1. Of these, a pen disclosed inPatent Document 1 includes a reception circuit configured to detectfalling edges and rising edges of a reception signal and restore awaveform of an uplink signal based on the detected falling edges andrising edges, thereby allowing to adequately restore the waveform of theuplink signal even if low frequency noise is superimposed on the uplinksignal.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: PCT Patent Publication WO2018/051388

Non Patent Document

Non Patent Document 1: Co-written by Mutsumi Hamaguchi, Michiaki Takeda,and Masayuki Miyamoto, “A 240 Hz-Reporting-Rate Mutual CapacitanceTouch-Sensing Analog Front-End Enabling Multiple Active/Passive Styluseswith 41 dB/32 dB SNR for 0.5 mm Diameter,” IEEE InternationalSolid-State Circuits Conference, 2015, p. 120-122

SUMMARY OF INVENTION Technical Problem

However, if there is dullness in the waveform of the uplink signal, itmay become difficult to detect the edges in the first place.Consequently, the waveform of the uplink signal cannot be restored evenwith the technique described in Patent Document 1.

Therefore, an object of the present invention is to provide a method forallowing a pen to properly receive an uplink signal even if there isdullness in a waveform of the uplink signal and to provide a pen.

Technical Solution

The present invention provides a method of transmitting transmissiondata from a sensor controller that detects a pen to the pen through asensor electrode group. The pen includes a pen tip electrode arrangednear a pen tip, an analog circuit that detects edges of a signal led tothe pen tip electrode, and a digital circuit that performs a correlationoperation of an output signal of the analog circuit and known patternsto detect the transmission data. The sensor controller is configured togenerate a pulse signal representing the transmission data, and transmitthe pulse signal by using a main signal and a sub signal of the pulsesignal so as to enhance the edges, thereby transmitting the transmissiondata through the sensor electrode group.

The present invention provides a pen that receives transmission datatransmitted through a sensor electrode group by a sensor controller thatdetects the pen. The pen includes a pen tip electrode arranged near apen tip, a differential circuit that detects edges of a signal led tothe pen tip electrode, a ΔΣ modulation unit that uses two referencepotentials corresponding to at least positive and negative values,respectively, to compare an output signal of the differential circuitand the two reference potentials and that executes feedback processingof comparison results, and a digital circuit that performs a correlationoperation of an output signal of the ΔΣ modulation unit and knownpatterns to detect the transmission data.

Advantageous Effects

According to the method of the present invention, the edges of theuplink signal are enhanced, and this increases the possibility that thepen can detect the edges even if there is dullness in the waveform ofthe uplink signal. Therefore, the pen can properly receive the uplinksignal.

According to the pen of the present invention, the edges can be surelydetected by the folding modulation executed by the ΔΣ modulation uniteven if there is dullness in the waveform of the uplink signal, and thisincreases the possibility that the pen can detect the edges. Therefore,the pen can properly receive the uplink signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a position detectionsystem 1 according to a first embodiment of the present invention.

FIG. 2(a) is a diagram illustrating a configuration example of an uplinksignal US, FIG. 2(b) is a diagram illustrating an example of a spreadcode corresponding to a preamble P, FIG. 2(c) is a diagram illustratinga chip sequence generated by a sensor controller 31 based ontransmission data after replacement with the spread code, FIG. 2(d) is adiagram illustrating a pulse signal generated by the sensor controller31 based on the chip sequence illustrated in FIG. 2(c), and FIG. 2(e) isa diagram illustrating an example of a reception waveform when a pen 2receives the pulse signal illustrated in FIG. 2(d).

FIG. 3 is a diagram illustrating a detailed configuration of a tablet 3.

FIG. 4 is a diagram illustrating an internal structure of the pen 2.

FIG. 5 is a schematic block diagram illustrating functional blocks ofthe pen 2.

FIG. 6(a) is a diagram illustrating part of a chip sequence (chipsequence after Manchester coding) generated by a spread processing unit51, FIG. 6(b) is a diagram illustrating a pulse signal generated by thespread processing unit 51 based on the chip sequence illustrated in FIG.6(a), FIG. 6(c) is a diagram illustrating a delay signal generated by atransmission processing unit 52 based on the pulse signal illustrated inFIG. 6(b), and FIGS. 6(d) and 6(e) are diagrams illustrating mixedsignals generated by the transmission processing unit 52 based on thepulse signal illustrated in FIG. 6(b).

FIG. 7 is a schematic circuit diagram illustrating a second modificationof the first embodiment of the present invention.

FIGS. 8(a) to 8(c) are the same diagrams as FIGS. 6(a) to 6(c), and FIG.8(d) is a diagram illustrating a mixed signal transmitted in the secondmodification of the first embodiment of the present invention.

FIG. 9 is a diagram illustrating a plurality of sensor electrodes 30Xaccording to a third modification of the first embodiment of the presentinvention.

FIG. 10 is a diagram illustrating a plurality of sensor electrodes 30Xand 30Y according to a fourth modification of the first embodiment ofthe present invention.

FIG. 11 is a diagram illustrating the uplink signal US transmitted bythe sensor controller 31 according to a fourth modification of the firstembodiment of the present invention.

FIG. 12 illustrates diagrams for describing a fifth modification of thefirst embodiment of the present invention.

FIG. 13 is a diagram illustrating a configuration of a reception circuit61 according to a second embodiment of the present invention.

FIG. 14A is a diagram specifically illustrating a circuit configurationof a comparison circuit 82 c according to the second embodiment of thepresent invention, and FIG. 14B is a diagram specifically illustrating acircuit configuration of the comparison circuit 82 c configured tocompare an output signal IO and four reference potentials VTP, VTP0,VTN0, and VTN.

FIG. 15(a) is a diagram illustrating an example of a chip sequencetransmitted by the sensor controller 31, FIG. 15(b) is a diagramillustrating an example of a reception signal Rx observed in the pen 2receiving the chip sequence illustrated in FIG. 15(a), FIG. 15(c) is adiagram illustrating an example of an output signal CO obtained from thereception signal Rx illustrated in FIG. 15(b), FIG. 15(d) is a diagramillustrating a chip sequence obtained from the output signal COillustrated in FIG. 15(c), FIG. 15(e) is a diagram illustrating apattern stored in a pattern storage unit 73 according to the chipsequence illustrated in FIG. 15(a), and FIG. 15(f) is a diagramexpressing the pattern illustrated in FIG. 15(e) by a pulse signal.

FIG. 16(a) is a diagram illustrating an example of a pulse signaltransmitted by the sensor controller 31, FIG. 16(b) is a diagramillustrating an output signal DO of an amplification circuit 81 outputin the pen 2 receiving the pulse signal illustrated in FIG. 16(a), FIG.16(c) is a diagram illustrating the output signal IO of an additioncircuit 82 b corresponding to the output signal DO illustrated in FIG.16(b), FIG. 16(d) is a diagram illustrating the output signal CO of ananalog circuit 71 corresponding to the output signal IO illustrated inFIG. 16(c), FIG. 16(e) is a diagram illustrating a known pattern storedin the pattern storage unit 73 according to the pulse signal illustratedin FIG. 16(a), and FIG. 16(f) is a diagram illustrating an output signalFO of an edge matched filter 87 corresponding to the output signal COillustrated in FIG. 16(d) and the pattern illustrated in FIG. 16(e).

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the attached drawings.

FIG. 1 is a diagram illustrating a configuration of a position detectionsystem 1 according to a first embodiment of the present invention. Asillustrated in FIG. 1 , the position detection system 1 includes a pen 2that is an active stylus and a tablet 3 that is a position detectionapparatus configured to detect a pen.

The tablet 3 includes a touch surface 3 a, a sensor electrode group 30arranged just below the touch surface 3 a, a sensor controller 31connected to the sensor electrode group 30, and a host processor 32 thatcontrols components of the sensor controller 31 including theseelements. In addition, the tablet 3 is connected to a charger 33(alternating current (AC) adapter), and the tablet 3 can be operated bypower supplied from a system power source through the charger 33.

When the pen 2 is near the touch surface 3 a, capacitance C is generatedbetween the pen 2 and the sensor electrode group 30. The pen 2 canexchange charge (form a capacitive coupling) through the capacitance tocommunicate with the sensor controller 31.

The communication between the pen 2 and the sensor controller 31 isbidirectional. FIG. 1 illustrates an uplink signal US transmitted fromthe sensor controller 31 to the pen 2 in the bidirectionalcommunication. The uplink signal US is a signal indicating aninstruction (command) for the pen 2, and the pen 2 that has received theuplink signal US executes a process according to the instructionindicated in the uplink signal US. When transmission of data isinstructed, the pen 2 acquires the instructed data and transmits thedata to the sensor controller 31 through a downlink signal. The datatransmitted in this way includes, for example, a unique identification(ID) of the pen 2, pen pressure indicating the pressure applied to thepen tip of the pen 2, on/off information of a switch provided on the pen2, and the like.

FIG. 2(a) is a diagram illustrating a configuration example of theuplink signal US. As illustrated in FIG. 2(a), the uplink signal USincludes six pieces of transmission data including two preambles P, dataD1 to D3 of 1 byte each, and an error detection code CRC. The sensorcontroller 31 uses a spread code with autocorrelation characteristics tospread each piece of the transmission data to generate a pulse signal.Further, the sensor controller 31 transmits the pulse signal through thesensor electrode group 30 to transmit the uplink signal US.

FIG. 2(b) is a diagram illustrating an example of the spread codecorresponding to the preamble P. Different spread codes corresponding tothe content (such as P, “0000,” and “0001”) of the transmission data arestored in advance in the sensor controller 31, and the sensor controller31 executes a process of replacing the transmission data with the spreadcode corresponding to the content. Although the number of chips includedin one spread code is 20 in the example illustrated in FIG. 2(b), it isobvious that the number of chips of the spread code is not limited to20.

FIG. 2(c) is a diagram illustrating a chip sequence generated by thesensor controller 31 based on the transmission data after replacementwith the spread code. As illustrated in FIG. 2(c), the sensor controller31 replaces “0” with “10” and replaces “1” with “01” in the spread codeto generate the chip sequence (Manchester coding). The replacement isperformed to prevent continuation of three or more chips of the samevalue.

FIG. 2(d) is a diagram illustrating a pulse signal generated by thesensor controller 31 based on the chip sequence illustrated in FIG.2(c). As illustrated in FIG. 2(d), the sensor controller 31 associates“1” with “high” and associates “0” with “low” in the chip sequence togenerate the pulse signal.

FIG. 2(e) is a diagram illustrating an example of a reception waveformwhen the pen 2 receives the pulse signal illustrated in FIG. 2(d). Asillustrated in FIG. 2(e), low frequency noise is superimposed on thepulse signal in some cases. Low frequency noise UN illustrated in FIG. 1is an example of the low frequency noise superimposed on the pulsesignal, and the low frequency noise UN is generated from the charger 33.In addition, low frequency noise from various noise sources existingaround the sensor controller 31 may be superimposed on the pulse signal.

When the low frequency noise is superimposed on the pulse signal, thereis dullness in the reception waveform as illustrated in FIG. 2(e). Whenthe degree of dullness is large, the restoration of the uplink signal USin the pen 2 is difficult. An object of the present invention is toallow the pen 2 to properly receive the uplink signal US even in such acase.

FIG. 3 is a diagram illustrating a detailed configuration of the tablet3. Hereinafter, a configuration and an operation of the tablet 3 will bedescribed in detail with reference to FIG. 3 .

The sensor electrode group 30 includes a plurality of sensor electrodes30X each extending in a Y-direction and a plurality of sensor electrodes30Y each extending in an X-direction, and the sensor electrode group 30is capacitive coupled to a pen tip electrode 21 (described later) of thepen 2 through the sensor electrodes 30X and 30Y. The transmission andthe reception of the uplink signal US and the downlink signal arerealized through the capacitive coupling. Hereinafter, the sensorelectrodes 30X and 30Y may be simply referred to as sensor electrodes 30when the sensor electrodes 30X and 30Y do not have to be particularlydistinguished.

The sensor controller 31 includes a micro control unit (MCU) 40, a logicunit 41, a transmission unit 42, a reception unit 43, and a selectionunit 44 as illustrated in FIG. 4 .

The MCU 40 and the logic unit 41 are control units that control thetransmission unit 42, the reception unit 43, and the selection unit 44to control transmission and reception operations of the sensorcontroller 31. More specifically, the MCU 40 is a microprocessor thatincludes a read-only memory (ROM) and a random access memory (RAM)inside and that operates based on a predetermined program. On the otherhand, the logic unit 41 is configured to generate control signals of thetransmission unit 42, the reception unit 43, and the selection unit 44based on the control of the MCU 40.

The MCU 40 has a function of receiving the downlink signal transmittedby the pen 2 through the reception unit 43 and a function of generatinga command cmd to be transmitted to the pen 2 and supplying the commandcmd to the transmission unit 42. The downlink signal includes a positionsignal that is an unmodulated carrier signal and includes a data signalincluding data corresponding to the command cmd. When the MCU 40receives a position signal from the pen 2, the MCU 40 calculatesposition coordinates (x, y) of the pen 2 on the touch surface 3 a fromthe reception strength in each of the plurality of sensor electrodes 30Xand 30Y included in the sensor electrode group 30 and outputs theposition coordinates (x, y) to the host processor 32. In addition, whenthe MCU 40 receives a data signal from the pen 2, the MCU 40 acquiresresponse data Res (specifically, unique ID, pen pressure, on/offinformation of switch, and the like) included in the data signal andoutputs the response data Res to the host processor 32.

The transmission unit 42 is a circuit that generates the uplink signalUS according to the control of the MCU 40 and the logic unit 41, and asillustrated in FIG. 4 , the transmission unit 42 includes a codesequence holding unit 50, a spread processing unit 51, and atransmission processing unit 52.

The code sequence holding unit 50 has a function of generating andholding the spread codes (spread codes with autocorrelationcharacteristics) based on the control signal supplied from the logicunit 41. The code sequence holding unit 50 is configured to generate andstore different spread codes corresponding to the content (such as P,“0000,” and “0001”) of the transmission data.

The spread processing unit 51 is a functional unit that generates thepulse signal illustrated in FIG. 2(d) based on the command cmd suppliedfrom the MCU 40. More specifically, the spread processing unit 51 firstgenerates the uplink signal US illustrated in FIG. 2(a) based on thecommand cmd. Further, for each of the plurality of pieces oftransmission data included in the uplink signal US, the spreadprocessing unit 51 selects one of the spread codes held by the codesequence holding unit 50 and uses the selected spread codes to spreadthe transmission data. As a result, the chip sequence illustrated inFIG. 2(b) is obtained. The spread processing unit 51 further executesthe Manchester coding to acquire the chip sequence illustrated in FIG.2(c). In addition, the spread processing unit 51 generates the pulsesignal illustrated in FIG. 2(d) based on the acquired chip sequence.

The transmission processing unit 52 is a functional unit that transmitsthe pulse signal generated by the spread processing unit 51 so as toenhance the edges. The “transmission of pulse signal so as to enhanceedges” in the present embodiment denotes using various methods describedlater to transmit the pulse signal so as to increase the numbers ofrising edges and falling edges included in the pulse signal. The detailswill be separately described later. However, other methods may be usedto transmit the pulse signal so as to enhance the edges.

The reception unit 43 is a circuit that receives the downlink signaltransmitted by the pen 2 based on the control signal supplied from thelogic unit 41. Specifically, the reception unit 43 is configured todecode the signal supplied from the selection unit 44 to generate adigital signal and configured to supply the digital signal as areception signal to the MCU 40.

The selection unit 44 includes switches 54 x and 54 y and conductorselection circuits 55 x and 55 y.

Each of the switches 54 x and 54 y is a switch element in which a commonterminal and one of a T terminal and an R terminal are connected. Thecommon terminal of the switch 54 x is connected to the conductorselection circuit 55 x, the T terminal is connected to an output end ofthe transmission unit 42, and the R terminal is connected to an inputend of the reception unit 43. In addition, the common terminal of theswitch 54 y is connected to the conductor selection circuit 55 y, the Tterminal is connected to the output end of the transmission unit 42, andthe R terminal is connected to the input end of the reception unit 43.

The conductor selection circuit 55 x is a switch element thatselectively connects the plurality of sensor electrodes 30X to thecommon terminal of the switch 54 x. The conductor selection circuit 55 xcan connect part or all of the plurality of sensor electrodes 30X at thesame time to the common terminal of the switch 54 x.

The conductor selection circuit 55 y is a switch element thatselectively connects the plurality of sensor electrodes 30Y to thecommon terminal of the switch 54 y. The conductor selection circuit 55 ycan also connect part or all of the plurality of sensor electrodes 30Yat the same time to the common terminal of the switch 54 y.

Four control signals sTRx, sTRy, selX, and selY are supplied from thelogic unit 41 to the selection unit 44. Specifically, the control signalsTRx is supplied to the switch 54 x, the control signal sTRy is suppliedto the switch 54 y, the control signal selX is supplied to the conductorselection circuit 55 x, and the control signal selY is supplied to theconductor selection circuit 55 y. The logic unit 41 uses the controlsignals sTRx, sTRy, selX, and selY to control the selection unit 44 torealize the transmission of the uplink signal US and the reception ofthe downlink signal transmitted by the pen 2.

More specifically, to transmit the uplink signal US, the logic unit 41controls the selection unit 44 to connect, to the output end of thetransmission unit 42, all of the plurality of sensor electrodes 30Y (orall of the plurality of sensor electrodes 30X) or a predetermined numberof the plurality of sensor electrodes 30X and 30Y near the position mostrecently derived for the pen 2 that receives the uplink signal US. Onthe other hand, the logic unit 41 in the case of receiving the positionsignal controls the selection unit 44 to sequentially connect, to theinput end of the reception unit 43, all of the plurality of sensorelectrodes 30X and 30Y (global scan) or a predetermined number of theplurality of sensor electrodes 30X and 30Y near the position derivedfrom the most recent position signal of the pen 2 that transmits theposition signal (local scan), while the transmission of the positionsignal is continuing. In this way, the MCU 40 can derive the position ofthe pen 2 based on the reception strength of the burst signal in eachsensor electrode 30. In addition, the logic unit 41 in the case ofreceiving the data signal controls the selection unit 44 to connect, tothe input end of the reception unit 43, a predetermined number of theplurality of sensor electrodes 30X and 30Y near the position derivedfrom the most recent position signal of the pen 2 that transmits thedata signal.

The configuration and the operation of the tablet 3 have been described.Next, a configuration and an operation of the pen 2 will be described indetail.

FIG. 4 is a diagram illustrating an internal configuration of the pen 2.As illustrated in FIG. 4 , the pen 2 includes a core (a central rod) 20,the pen tip electrode 21, a pen pressure detection sensor 23, a circuitboard 24, and a battery 25. Although not illustrated, the pen 2 furtherincludes, on a side surface or a bottom surface of a housing, a switchthat can be operated by the user.

The core 20 is a rod-shaped member, and the core 20 is arranged so thata pen holder direction of the pen 2 and a longitudinal direction of thecore 20 coincide with each other. The pen tip electrode 21 is aconductor arranged near the pen tip, and the pen tip electrode 21includes, for example, a conductive substance embedded inside the core20. In another example, a conductive material may be applied to thesurface of the tip portion of the core 20 to provide the pen tipelectrode 21.

The pen pressure detection sensor 23 is physically connected to the core20, and the pen pressure detection sensor 23 can detect the pen pressureapplied to the tip of the core 20. Specifically, a variable capacitor inwhich the capacitance changes according to the pen pressure can be usedas the pen pressure detection sensor 23.

The pen tip electrode 21 is electrically connected to the circuit board24, and the pen tip electrode 21 plays a role of receiving the uplinksignal US transmitted by the tablet 3 to supply the uplink signal US tothe circuit board 24 and transmitting the downlink signal supplied fromthe circuit board 24 toward the tablet 3. Although the pen tip electrode21 performs both the transmission and the reception here, an electrodefor transmission and an electrode for reception may be separatelyprovided. The battery 25 is a power source that supplies operating powerto each of these elements and the like in the circuit board 24.

FIG. 5 is a schematic block diagram illustrating functional blocks ofthe pen 2. The functional blocks illustrated in FIG. 5 are realized byelectronic circuits formed on the circuit board 24.

As illustrated in FIG. 5 , the pen 2 functionally includes a switch 60,a reception circuit 61, a controller 62, and a transmission circuit 63.

The switch 60 is a switch element in which a common terminal and one ofa T terminal and an R terminal are connected. The common terminal of theswitch 60 is connected to the pen tip electrode 21, the T terminal isconnected to an output end of the transmission circuit 63, and the Rterminal is connected to an input end of the reception circuit 61. Theconnection state of the switch 60 is controlled by the controller 62.The controller 62 controls the switch 60 to connect the common terminaland the R terminal in the case of the reception of the uplink signal USfrom the sensor controller 31 and controls the switch 60 to connect thecommon terminal and the T terminal in the case of the transmission ofthe downlink signal (position signal or data signal) toward the sensorcontroller 31.

The reception circuit 61 is a circuit that demodulates the signalreceived through the pen tip electrode 21 and the switch 60 to acquirethe uplink signal US and that outputs the uplink signal US to thecontroller 62. An analog circuit 71, a digital circuit 72, and a patternstorage unit 73 are provided inside the reception circuit 61 asillustrated in FIG. 5 .

The analog circuit 71 includes an edge detection circuit that detectsedges included in the signal supplied from the switch 60 (signal led tothe pen tip electrode 21) and a waveform restoration circuit thatrestores the waveform from the edges detected by the edge detectioncircuit. Although the specific configuration of each circuit is notlimited, for example the edge detection circuit can include adifferential circuit that generates a differential signal of the signalsupplied from the switch 60, a positive direction pulse detectioncircuit that detects rising edges of the differential signal, and anegative direction pulse detection circuit that detects falling edges ofthe differential signal. In addition, the waveform restoration circuitcan include an SR latch circuit including an S input that receives anoutput signal of the positive direction pulse detection circuit and an Rinput that receives an output signal of the negative direction pulsedetection circuit. The signal output from the waveform restorationcircuit is included in the output signal of the analog circuit 71, andideally, the signal has the same waveform as the waveform of the pulsesignal generated by the spread processing unit 51 of the sensorcontroller 31 (see FIG. 2(d)).

The digital circuit 72 is a circuit that performs correlation operationof the output signal of the analog circuit 71 and known patterns storedin the pattern storage unit 73 to detect the transmission datatransmitted by the sensor controller 31.

More specifically, a plurality of chip sequences are first stored asknown patterns in the pattern storage unit 73. Each chip sequence is achip sequence of two values including a plurality of chips, each with avalue of 0 or 1. The chip sequences are obtained by applying Manchestercoding to each of the plurality of spread codes that may be used by thesensor controller 31 to transmit the uplink signal US.

The digital circuit 72 includes a first-in first-out shift register thatcan store chip sequences corresponding to the number of chips in onespread code, and the digital circuit 72 stores the output signal of theanalog circuit 71 in the shift register every time the digital circuit72 acquires one chip. Further, every time the digital circuit 72 storesone new chip, the digital circuit 72 calculates the correlation betweenthe chip sequence stored in the shift register at that point and each ofthe plurality of known patterns stored in the pattern storage unit 73.As a result, when the calculation result for a certain pattern is equalto or greater than a predetermined value, the digital circuit 72determines that the spread code corresponding to the pattern isdetected. The digital circuit 72 restores the uplink signal US based onthe spread codes detected one after another in this way and outputs theuplink signal US to the controller 62.

The controller 62 is a processor including a memory inside, and thecontroller 62 operates according to a program stored in the memory.

The operation performed by the controller 62 includes a processcorresponding to the uplink signal US supplied from the receptioncircuit 61. More specifically, the controller 62 executes a process ofdetermining a transmission and reception schedule of various signalsaccording to the uplink signal US supplied from the reception circuit 61and controlling the connection state of the switch 60 according to thetransmission and reception schedule. That is, as described above, thecontroller 62 controls the switch 60 to connect the common terminal andthe R terminal in the case of the reception of the uplink signal US fromthe sensor controller 31 and controls the switch 60 to connect thecommon terminal and the T terminal in the case of the transmission ofthe signal (position signal or data signal) toward the sensor controller31.

The controller 62 executes a process of instructing the transmissioncircuit 63 to transmit the position signal at transmission timing of theposition signal indicated in the determined transmission and receptionschedule. In addition, when the command indicated in the uplink signalUS supplied from the reception circuit 61 indicates a transmissioninstruction of various types of data (such as unique ID, pen pressure,and on/off information of switch), the controller 62 executes a processof acquiring the instructed data and supplying the data as transmissiondata to the transmission circuit 63 at the transmission timing of thedata signal indicated in the determined transmission and receptionschedule.

The transmission circuit 63 includes an oscillation circuit of apredetermined carrier signal, and when the controller 62 instructs thetransmission circuit 63 to transmit the position signal, thetransmission circuit 63 supplies the carrier signal to the pen tipelectrode 21 without modulation. On the other hand, when thetransmission data is supplied from the controller 62, the transmissioncircuit 63 uses the supplied transmission data to modulate the carriersignal and supplies the modulated carrier signal to the pen tipelectrode 21.

Next, the process of “transmission of pulse signal so as to enhanceedges” executed by the transmission processing unit 52 illustrated inFIG. 3 will be described in detail.

FIG. 6(a) is a diagram illustrating part of a chip sequence (chipsequence after Manchester coding) generated by the spread processingunit 51, and FIG. 6(b) is a diagram illustrating a pulse signal (mainsignal) generated by the spread processing unit 51 based on the chipsequence. An illustrated chip length T indicates the time length of eachchip (time length of one chip) included in the spread code before theManchester coding.

FIGS. 6(c) and 6(d) are diagrams illustrating a delay signal (subsignal) and a mixed signal generated by the transmission processing unit52 based on the pulse signal illustrated in FIG. 6(b), respectively. Thetransmission processing unit 52 that has received the pulse signal fromthe spread processing unit 51 first changes the edge timing of the pulsesignal to generate the delay signal illustrated in FIG. 6(c). Morespecifically, the transmission processing unit 52 delays the pulsesignal by a time (T/4 in the example of FIG. 6(c)) shorter than a halfT/2 the chip length T to generate the delay signal.

Next, the transmission processing unit 52 generates the mixed signalillustrated in FIG. 6(d) based on the pulse signal illustrated in FIG.6(b) and the delay signal illustrated in FIG. 6(c). The mixed signalgenerated in this way is a signal including two corresponding edges (forexample, illustrated edges E1 and E2) in the time shorter than the halfT/2 the chip length T starting at each edge of the pulse signal.Although two edges are included here, the number of delay signals may beincreased to provide three or more corresponding edges. It is morepreferable to provide an even number of corresponding edges.

Here, as can be understood from FIG. 6(d), the mixed signal generated bythe transmission processing unit 52 according to the present embodimentincludes a return edge (for example, illustrated edge E3) in theopposite direction of the corresponding edges in the time shorter thanthe half T/2 the chip length T starting at each edge of the pulsesignal. If the mixed signal is transmitted from the sensor electrodegroup 30 in this state, the edge detection circuit in the analog circuit71 also detects the return edge as an edge, and as a result, a wrongwaveform may be restored. Therefore, as illustrated in FIG. 6(e), thetransmission processing unit 52 may set the slope of the return edge toa slope gentler than the slope of each edge of the pulse signal. Thisreduces the possibility that the edge detection circuit in the analogcircuit 71 will detect the return edge as an edge, and the possibilityof the restoration of a wrong waveform can be reduced.

As described above, according to the transmission method of the uplinksignal US of the present embodiment, the edges received by the pen 2 canbe increased to enhance the edges of the uplink signal US. Thisincreases the possibility that the pen can detect the edges even ifthere is dullness in the waveform of the uplink signal US, and the pen 2can properly receive the uplink signal US.

Note that there can be various modifications of the present embodiment.Hereinafter, the modifications will be described one by one.

In a first modification of the present embodiment, a pulse signal thatis a main signal generated by the spread processing unit 51 and a subsignal generated by the transmission processing unit 52 based on thepulse signal are transmitted from different sensor electrodes 30 totransmit a mixed signal. The sensor controller 31 in this case isconfigured to supply the main signal and the sub signal created by thetransmission processing unit 52 to different sensor electrodes 30.Therefore, the sub signal according to the present modification is adifferent electrode signal transmitted from a sensor electrode 30different from the sensor electrode 30 for the main signal. However, itis preferable that the content of the sub signal includes the same delaysignal as the delay signal of the present embodiment. In this way, themixed signal can be transmitted without generating the mixed signalillustrated in FIG. 6(d) or 6(e).

FIG. 7 is a schematic circuit diagram illustrating a second modificationof the present embodiment. A signal source 51A illustrated in FIG. 7indicates a pulse signal (main signal) generated by the spreadprocessing unit 51, and a signal source 52A illustrates a sub signalgenerated by the transmission processing unit 52. The tablet 3 accordingto the present modification is configured to use both of the layeredsensor electrodes 30X and 30Y to transmit the main signals and the subsignals to transmit mixed signals. Specifically, the tablet 3 isconfigured to transmit the main signals from at least part of the sensorelectrodes 30Y arranged in a first layer and transmit the sub signalsfrom at least part of the sensor electrodes 30X arranged in a secondlayer different from the first layer.

The sub signal according to the present embodiment is a differentelectrode signal as in the first modification, and the content of thesub signal may include the same delay signal as the delay signal of thepresent embodiment or may include a signal exactly the same as the mainsignal. The former case can obtain an advantageous effect of increasingthe edges received by the pen 2 as in the present embodiment. The samesignals are transmitted from two layers in the latter case, and thelatter case can obtain an advantageous effect of enhancing the edgescompared to when the signals are transmitted from only one layer.

FIG. 8(d) is a diagram illustrating a mixed signal transmitted in thepresent modification when the delay signal of the main signal is the subsignal. Note that FIGS. 8(a) to 8(c) are the same diagrams as FIGS. 6(a)to 6(c). As illustrated in FIG. 8(d), the mixed signal according to thepresent modification is a sum of the pulse signal and the delay signal.As can be understood from FIG. 8(d), this can also increase the numberof edges received by the pen 2 to enhance the edges of the uplink signalUS. In addition, according to the present modification, the return edgeis not generated, and this can reduce the possibility that the analogcircuit 71 will restore a wrong waveform.

The present modification can also be advantageously applied to a case inwhich the tablet 3 is a position detection apparatus of what isgenerally called an in-cell system. The in-cell system is a system inwhich an electrode (typically, common electrode of liquid crystaldisplay or negative electrode of organic electroluminescence (EL)display) supplied with potential necessary for driving the pixel of thedisplay apparatus arranged on top of the sensor electrode group 30 isused as one of the sensor electrodes 30X and 30Y. Therefore, when thepresent modification is applied to the in-cell tablet 3, one of the mainsignal and the sub signal is transmitted from, for example, one of thesensor electrodes 30X and 30Y that is the common electrode of the liquidcrystal display, and the other of the main signal and the sub signal istransmitted from the other of the sensor electrodes 30X and 30Y. As inthe present modification, this case can also obtain an advantageouseffect of enhancing the edges of the uplink signal US and anadvantageous effect of reducing the possibility that the analog circuit71 will restore a wrong waveform.

FIG. 9 is a diagram illustrating the plurality of sensor electrodes 30Xaccording to a third modification of the present embodiment. The tablet3 according to the present modification classifies the plurality ofsensor electrodes 30X into a plurality of first sensor electrodesbelonging to an illustrated group G1 and a plurality of second sensorelectrodes (sensor electrodes 30X belonging to group G2) arranged atpositions not overlapping the plurality of first sensor electrodes inplan view. In addition, the transmission processing unit 52 isconfigured to transmit the pulse signal through the plurality of firstsensor electrodes and transmit a reverse-phase signal of the pulsesignal through the plurality of second sensor electrodes. This canprevent the uplink signal US from changing the ground potential of thepen 2 through the hand of the person holding the pen 2 so that the pen 2cannot detect the uplink signal US when, for example, the hand of theperson is in contact with the touch surface 3 a.

FIG. 10 is a diagram illustrating the plurality of sensor electrodes 30Xand 30Y according to a fourth modification of the present embodiment. Inaddition, FIG. 11 is a diagram illustrating the uplink signals UStransmitted by the sensor controller 31 according to the presentmodification. First, with reference to FIG. 10 , the sensor controller31 according to the present modification first determines a region R inwhich the uplink signals US are transmitted. Although part of the touchsurface 3 a is the region R in the example depicted in FIG. 10 , theentire touch surface 3 a may be the region R.

The sensor controller 31 that has determined the region R classifies theplurality of sensor electrodes 30 going through the region R into aplurality of groups so that the sensor electrodes 30 close to each otherbelong to different groups as much as possible. FIG. 10 illustrates anexample of the groups classified in this way. In the example, the sensorelectrodes 30Y are alternately classified into a group A and a group B,and the sensor electrodes 30X are alternately classified into a group Cand a group D.

FIG. 11 illustrates an example of a case of using the groups A to Dillustrated in FIG. 10 to transmit the uplink signal US. Although eachof five pieces of transmission data “8,” “5,” “7,” “9,” and “3” istransmitted through a chip sequence of eight chips (chip sequenceobtained by applying Manchester coding to each of four bits indicatingeach piece of transmission data) for the simplification of thedescription in the example illustrated in FIG. 11 , actually the spreadcode may be used to transmit the data as in the present embodiment.

The sensor controller 31 according to the present modification isconfigured to divide eight chips included in one piece of transmissiondata into first four chips and second four chips and disperse four edges(rising edges U and falling edges D) of the pulse signal correspondingto the chips to four groups A to D to transmit the transmission data asillustrated in FIG. 11 . In this way, the pen 2 positioned in the regionR can receive all of the edges and can receive the uplink signal US.However, the pen 2 not positioned in the region R cannot receive part orall of the edges and cannot receive the uplink signal US (even if onlypart of the edges can be received, the received part is discarded as aresult of the error detection using the error detection code CRCillustrated in FIG. 2(a)). Therefore, according to the presentmodification, the region in the touch surface 3 a can be limited totransmit the uplink signal US. The present modification can be appliedto transmit the uplink signal US while limiting the pens 2 that receivethe uplink signal US when, for example, a plurality of pens 2 arepositioned in the touch surface 3 a.

FIG. 12 illustrates diagrams for describing a fifth modification of thepresent embodiment. Note that FIGS. 12(a) and 12(b) are the samediagrams as FIGS. 6(a) and 6(d).

The pulse signal illustrated in FIG. 12(b) represents the chip sequenceillustrated in FIG. 12(a), and it can also be stated that the pulsesignal represents the chip sequence illustrated in FIG. 12(c). Thisindicates that one pulse signal can be used to transmit two types ofdata depending on the method of processing in the pen 2. Therefore, inthe present modification, two types of patterns including first andsecond patterns described below are prepared as known patterns used bythe pen 2 in the correlation operation to allow the pen 2 to selectivelyreceive two types of data.

The first pattern is a pattern in which the time length of one chip isrelatively long. The digital circuit 72 (FIG. 5 ) of the pen 2 using thefirst pattern applies a correlation operation with relatively coarsegranularity to the output signal of the analog circuit 71 to restore thechip sequence illustrated in FIG. 12(a) from the pulse signalillustrated in FIG. 12(b).

The second pattern is a pattern in which the time length of one chip isrelatively short. The digital circuit 72 (FIG. 5 ) of the pen 2 usingthe second pattern applies a correlation operation with relatively finegranularity to the output signal of the analog circuit 71 to restore thechip sequence illustrated in FIG. 12(c) from the pulse signalillustrated in FIG. 12(b).

In this way, according to the present modification, two types ofpatterns with different time lengths of one chip are prepared as knownpatterns used by the pen 2 in the correlation operation. This can obtainan advantageous effect that one uplink signal US can be used to allowthe pen 2 to selectively receive two types of data. Note that in thepresent modification, the time length per chip of the pattern stored inthe pattern storage unit 73 illustrated in FIG. 5 may vary depending onthe pen 2. In this way, the sensor controller 31 can use one uplinksignal US to transmit different data to two pens 2.

Next, the position detection system 1 according to a second embodimentof the present invention will be described. In the position detectionsystem 1 according to the present embodiment, the reception method ofthe uplink signal US executed by the reception circuit 61 is differentfrom that of the first embodiment. That is, in the reception circuit 61according to the present embodiment, ΔΣ modulation is performed in theanalog circuit 71, and correlation operation based on three values of+1, 0, and −1 is performed in the digital circuit 72. The positiondetection system 1 according to the second embodiment is similar to theposition detection system 1 according to the first embodiment in otherrespects. Therefore, the same reference signs are assigned to the samecomponents, and the differences from the position detection system 1according to the first embodiment will be mainly described below.

FIG. 13 is a diagram illustrating a configuration of the receptioncircuit 61 according to the present embodiment. As illustrated in FIG.13 , the reception circuit 61 according to the present embodimentincludes a pulse density detection unit 74 and an MCU 75 in addition tothe analog circuit 71, the digital circuit 72, and the pattern storageunit 73 as also illustrated in FIG. 5 .

The analog circuit 71 according to the present embodiment includes ahigh-pass filter 80 with an input end connected to the R terminal of theswitch 60 (see FIG. 5 ), an amplification circuit 81 that amplifies anoutput signal of the high-pass filter 80, and a ΔΣ modulation unit 82.The high-pass filter 80 is a circuit configured to pass only frequencycomponents equal to or higher than a cutoff frequency. The cutofffrequency of the high-pass filter 80 can be controlled by the MCU 75.The amplification circuit 81 is a circuit that amplifies the outputsignal of the high-pass filter 80 and that supplies the output signal asan output signal DO to the ΔΣ modulation unit 82. The amplificationcircuit 81 includes a variable gain amplifier in which the amplificationfactor can be controlled by the MCU 75. The high-pass filter 80 and theamplification circuit 81 function as a differential circuit that detectsedges of the signal (reception signal Rx) led to the pen tip electrode21 (see FIG. 5 ).

The ΔΣ modulation unit 82 is a functional unit that uses at least tworeference potentials VTP and VTN corresponding to positive and negativevalues to compare the output signal DO of the amplification circuit 81and the reference potentials VTP and VTN and that executes feedbackprocessing of the comparison results. As illustrated in FIG. 13 , the ΔΣmodulation unit 82 includes a subtraction circuit 82 a, an additioncircuit 82 b, a comparison circuit 82 c, and delay circuits 82 d and 82e.

The comparison circuit 82 c is a circuit that compares an output signalIO of the addition circuit 82 b and the predetermined referencepotentials VTP and VTN (VTP=−VTN>0), and the comparison circuit 82 cincludes three output terminals including an output terminal ofcomparison result, a positive-side output terminal (+1), and anegative-side output terminal (−1). Of these, a signal output from theoutput terminal of comparison result provides an output signal CO of theanalog circuit 71.

When the output signal IO of the addition circuit 82 b is higher thanthe reference potential VTP, the comparison circuit 82 c outputs +1 forthe output signal CO, sets the potential of the positive-side outputterminal to high, and sets the potential of the negative-side outputterminal to low. In addition, when the output signal IO of the additioncircuit 82 b is lower than the reference potential VTN, the comparisoncircuit 82 c outputs −1 for the output signal CO, sets the potential ofthe negative-side output terminal to high, and sets the potential of thepositive-side output terminal to low. In other cases, the comparisoncircuit 82 c outputs 0 for the output signal CO and sets both potentialsof the positive-side output terminal and the negative-side outputterminal to low. As a result of the process executed by the comparisoncircuit 82 c, the output signal CO is a pulse signal with three valuesof +1, 0, and −1.

The comparison circuit 82 c operates at a cycle (for example, T/8)shorter than the chip length (half T/2 the chip length T illustrated inFIG. 6 ) of the chip sequence transmitted by the sensor controller 31.Therefore, the output signal CO is a pulse signal including a pluralityof chips (for example, four chips) with respect to one chip of the chipsequence transmitted by the sensor controller 31.

FIG. 14A is a diagram specifically illustrating a circuit configurationof the comparison circuit 82 c according to the present embodiment. Asillustrated in FIG. 14A, the comparison circuit 82 c includes acomparator CPa corresponding to a positive value, a comparator CPbcorresponding to a negative value, and an output circuit 100. The outputterminal of the comparator CPa is connected as the positive-side outputterminal (+1) to the delay circuit 82 d and to the output circuit 100.In addition, the output terminal of the comparator CPb is connected asthe negative-side output terminal (−1) to the delay circuit 82 e and tothe output circuit 100.

The output signal IO of the addition circuit 82 b is supplied in commonto one input terminal of each of the comparators CPa and CPb. On theother hand, the reference potentials VTP and VTN are supplied to theother input terminals of the comparators CPa and CPb, respectively. Inaddition, each of the comparators CPa and CPb is configured to execute acomparison operation at timing synchronized with a clock CK1 suppliedfrom a clock circuit not illustrated. The clock CK1 oscillates at acycle (for example, T/8) shorter than the chip length (half T/2 the chiplength T illustrated in FIG. 6 ) of the chip sequence transmitted by thesensor controller 31. As a result, the output signal CO is a pulsesignal including a plurality of chips (for example, four chips) withrespect to one chip of the chip sequence transmitted from the sensorcontroller 31 as described above.

The comparator CPa is configured to output “high” when the output signalIO of the addition circuit 82 b is larger than the reference potentialVTP and output “low” otherwise. In addition, the comparator CPb isconfigured to output “low” when the output signal IO of the additioncircuit 82 b is larger than the reference potential VTN and output“high” otherwise. In this way, the comparison results of the comparisoncircuit 82 c are fed back in three values (that is, +1, 0, and −1) tothe subtraction circuit 82 a.

The output circuit 100 is a circuit that generates the output signal COof the ΔΣ modulation unit 82 based on the output of the comparators CPaand CPb. Specifically, the output circuit 100 sets the output signal COto +1 when the output of the comparator CPa is high, sets the outputsignal CO to −1 when the output of the comparator CPb is high, and setsthe output signal CO to 0 in other cases. This realizes the outputsignal CO that is a pulse signal with three values of +1, 0, and −1.

Although the comparison circuit 82 c of FIG. 14A compares the outputsignal IO and two reference potentials VTP and VTN here, more referencepotentials may be used for the comparison. Specifically, the comparisoncircuit 82 c may compare, for example, the output signal IO and fourreference potentials VTP, VTP0, VTN0, and VTN(VTP=−VTN=2×VTP0=−2×VTN0>0). In this case, the comparison results of thecomparison circuit 82 c are fed back in five values (that is, +2, +1, 0,−1, and −2) to the subtraction circuit 82 a. On the other hand, althoughthe details will be described later, the output signal CO of the analogcircuit 71 is output in three values (that is, +1, 0, and −1) even whenthe comparison circuit 82 c compares the output signal IO and fourreference potentials VTP, VTP0, VTN0, and VTN. The details will now bedescribed.

FIG. 14B is a diagram specifically illustrating the circuitconfiguration of the comparison circuit 82 c configured to compare theoutput signal IO and four reference potentials VTP, VTP0, VTN0, and VTN.As illustrated in FIG. 14B, the comparison circuit 82 c in this caseincludes two comparators CPa and CPc corresponding to positive values,two comparators CPb and CPd corresponding to negative values, and theoutput circuit 100. The output terminal of the comparator CPa isconnected as the positive-side output terminal (+2) to the delay circuit82 d and to the output circuit 100. In addition, the output terminal ofthe comparator CPb is connected as the negative-side output terminal(−2) to the delay circuit 82 e and to the output circuit 100. The outputterminal of the comparator CPc is connected as the positive-side outputterminal (+1) to the delay circuit 82 d and to the output circuit 100,and the output terminal of the comparator CPd is connected as thenegative-side output terminal (−1) to the delay circuit 82 e and to theoutput circuit 100.

The output signal IO of the addition circuit 82 b is supplied in commonto one input terminal of each of the comparators CPa to CPd. On theother hand, the reference potentials VTP, VTN, VTP0, and VTN0 aresupplied to the other input terminals of the comparators CPa to CPd,respectively. The comparators CPa to CPd operate at the timingsynchronized with the clock CK1, and this is similar to the case of FIG.14A.

The comparator CPa is configured to output “high” when the output signalIO of the addition circuit 82 b is larger than the reference potentialVTP and output “low” otherwise. The comparator CPb is configured tooutput “low” when the output signal IO of the addition circuit 82 b islarger than the reference potential VTN and output “high” otherwise. Thecomparator CPc is configured to output “high” when the output signal IOof the addition circuit 82 b is larger than the reference potential VTP0and output “low” otherwise. The comparator CPd is configured to output“low” when the output signal IO of the addition circuit 82 b is higherthan the reference potential VTN0 and output “high” otherwise. In thisway, the comparison results of the comparison circuit 82 c are fed backin five values (that is, +2, +1, 0, −1, and −2) to the subtractioncircuit 82 a.

The output circuit 100 is configured to generate the output signal CO ofthe ΔΣ modulation unit 82 based on the output of the comparators CPa andCPb. Specifically, the output circuit 100 sets the output signal CO to+1 when the output of the comparator CPa is high, sets the output signalCO to −1 when the output of the comparator CPb is high, and sets theoutput signal CO to 0 in other cases. The output of the comparators CPcand CPd is not referenced in generating the output signal CO. Thisrealizes the output signal CO that is a pulse signal with three valuesof +1, 0, and −1 even though five values are fed back to the subtractioncircuit 82 a. In this way, the output signal CO includes three values,and this can reduce the scale of the circuit necessary for thecorrelation operation.

Note that the output circuit 100 may also refer to the output of thecomparators CPc and CPd so that the output signal CO includes a pulsesignal of five values (that is, +2, +1, 0, −1, and −2). When the outputsignal CO includes five values in this way, there is an advantageouseffect that the digital circuit 72 (see FIG. 13 ) in a later stage canalso take the level values into account to derive the correlationvalues.

FIG. 13 will be further described. The delay circuit 82 d plays a roleof multiplying the potential of the positive-side output terminal of thecomparison circuit 82 c by Δ, delaying the signal by, for example, oneclock (one chip of output signal CO), and feeding back the signal to thesubtraction circuit 82 a. Similarly, the delay circuit 82 e plays a roleof multiplying the potential of the negative-side output terminal of thecomparison circuit 82 c by −Δ, delaying the signal by, for example, oneclock, and feeding back the signal to the subtraction circuit 82 a. Notethat it is preferable that the specific value of Δ be a value equal toVTP in the case of the feedback in three values and equal to VTP0 in thecase of the feedback in five values.

The subtraction circuit 82 a is a circuit that outputs a signal obtainedby subtracting the amount of potential corresponding to the outputsignals of the delay circuits 82 d and 82 e from the output signal DO ofthe amplification circuit 81. As a result of the subtraction, thepotential level of the input signal of the addition circuit 82 b dropswhen the output signal IO of the previous clock is higher than thereference potential VTP, and the potential level of the input signal ofthe addition circuit 82 b rises when the output signal IO of theprevious clock is lower than the reference potential VTN. Therefore,there is an advantageous effect that the potential level of the outputsignal IO of the addition circuit 82 b falls within a certain range.

The addition circuit 82 b is a circuit that outputs a signal obtained byintegrating the output signal of the subtraction circuit 82 a. Theoutput signal IO of the addition circuit 82 b is obtained by adding theoutput signal of the subtraction circuit 82 a to the output signal ofthe addition circuit 82 b of the previous clock.

FIG. 15(a) is a diagram illustrating an example of the chip sequence(illustrated in FIG. 2(c)) transmitted by the sensor controller 31. FIG.15(b) is a diagram illustrating an example of the reception signal Rxobserved in the pen 2 receiving the chip sequence. FIG. 15(c) is adiagram illustrating an example of the output signal CO obtained fromthe reception signal Rx. FIG. 15(d) is a diagram illustrating a chipsequence obtained from the output signal CO. Note that low frequencynoise that is a sine wave is superimposed on the reception signal Rxillustrated in FIG. 15(b). As can be understood from these drawings, theoutput signal CO of the case in which the low frequency noise issuperimposed on the reception signal Rx is a pulse signal thatoscillates more intensely than the reception signal Rx. This indicatesthat the ΔΣ modulation unit 82 is more sensitively detecting the changein the reception signal Rx.

FIG. 13 will be further described. The pattern storage unit 73 accordingto the present embodiment is configured to store, as a known pattern, achip sequence of three values including a plurality of chips with valuesof +1, 0, and −1, for each of a plurality of spread codes that may beused by the sensor controller 31 to transmit the uplink signal US.

FIG. 15(e) is a diagram illustrating a pattern stored in the patternstorage unit 73 according to the chip sequence illustrated in FIG.15(a), and FIG. 15(f) is a diagram expressing the pattern by a pulsesignal. As can be understood from FIGS. 15(d) and 15(e), the patternstored in the pattern storage unit 73 is a chip sequence including onechip with respect to one chip of the output signal CO. In addition, ascan be understood from FIGS. 15(a) and 15(e), the pattern stored in thepattern storage unit 73 is a chip sequence of three values, in whichonly one chip becomes “−1” according to the change from “+1” to “0” inthe transmission chip sequence, only one chip becomes “+1” according tothe change from “0” to “+1” in the transmission chip sequence, and theother chips are “0.”

FIG. 13 will be further described. The digital circuit 72 according tothe present embodiment includes an edge matched filter 87 and an uplinksignal restoration unit 88.

The edge matched filter 87 includes a first-in first-out shift registerthat can store chip sequences corresponding to the number of chips inone spread code, and the edge matched filter 87 stores the output signalCO of the analog circuit 71 in the shift register every time the edgematched filter 87 acquires one chip. Further, every time the edgematched filter 87 stores one new chip, the edge matched filter 87calculates the correlation between the chip sequence stored in the shiftregister at that point and each of the plurality of known patternsstored in the pattern storage unit 73. The edge matched filter 87sequentially supplies the results as output signals FO to the uplinksignal restoration unit 88.

The uplink signal restoration unit 88 determines that the spread codecorresponding to the pattern used to calculate the output signal FO isdetected when the output signal FO is equal to or greater than apredetermined value. Further, the uplink signal restoration unit 88restores the uplink signal US based on the spread codes detected oneafter another and outputs the uplink signal US to the controller 62.

The pulse density detection unit 74 is a functional unit that detectsthe pulse density of the output signal CO of the ΔΣ modulation unit 82and notifies the MCU 75 of the result. In addition, the MCU 75 is anintegrated circuit (control circuit) included in a microprocessor to beembedded, and the MCU 75 plays a role of controlling the gain of theamplification circuit 81 based on the pulse density notified from thepulse density detection unit 74 and controlling the cutoff frequency ofthe high-pass filter 80.

Here, the gain control of the amplification circuit 81 based on thepulse density will be described. When the absolute value of the inputsignal of the ΔΣ modulation unit 82 (output signal DO of amplificationcircuit 81) is too large, the output signal IO of the addition circuit82 b is always higher than the reference potential VTP or lower than thereference potential VTN. As a result, the output signal CO is fixed to“+1” or “−1,” and the edge detection of the ΔΣ modulation unit 82 doesnot function. Conversely, when the absolute value of the input signal ofthe ΔΣ modulation unit 82 (output signal DO of amplification circuit 81)is too small, the state that the output signal IO of the additioncircuit 82 b is between the reference potential VTP and the referencepotential VTN continues. The output signal CO is fixed to “0,” and theedge detection of the ΔΣ modulation unit 82 also does not function.Therefore, the MCU 75 lowers or raises the gain of the amplificationcircuit 81 according to the value of the output signal DO when the pulsedensity notified from the pulse density detection unit 74 is equal to orsmaller than a predetermined value. The potential level of the outputsignal DO drops when the gain of the amplification circuit 81 islowered, and this can release the fixation of the output signal CO fixedto “+1” or “−1.” In addition, the potential level of the output signalDO rises when the gain of the amplification circuit 81 is raised, andthis can release the fixation of the output signal CO fixed to “0.”

FIG. 16(a) is a diagram illustrating an example of a pulse signaltransmitted by the sensor controller 31. FIG. 16(b) is a diagramillustrating the output signal DO of the amplification circuit 81 outputin the pen 2 receiving the pulse signal. FIG. 16(c) is a diagramillustrating the output signal IO of the addition circuit 82 bcorresponding to the output signal DO. FIG. 16(d) is a diagramillustrating the output signal CO of the analog circuit 71 correspondingto the output signal IO. FIG. 16(e) is a diagram illustrating a knownpattern stored in the pattern storage unit 73 according to the pulsesignal illustrated in FIG. 16(a). FIG. 16(f) is a diagram illustratingthe output signal FO of the edge matched filter 87 corresponding to theoutput signal CO illustrated in FIG. 16(d) and the pattern illustratedin FIG. 16(e). Hereinafter, the effects of the present embodiment willbe described in detail with reference to these drawings along with FIG.13 . Here, FIGS. 16(c) and FIG. 16(d) illustrate a case of using thecomparison circuit 82 c illustrated in FIG. 14B.

The output signal DO of the amplification circuit 81 is a signaltemporarily increasing toward the plus side according to the risingedges of the pulse signal transmitted by the sensor controller 31 andtemporarily increasing toward the minus side according to the fallingedges as illustrated in FIG. 16(b). This is because the high-pass filter80 illustrated in FIG. 13 functions as a differential circuit.

The output signal IO of the addition circuit 82 b is a signal foldedwhen the signal exceeds the reference potentials VTP and VTP0 and whenthe signal falls below the reference potentials VTN0 and VTN asillustrated in FIG. 16(c). Because of the folding, it can be stated thatthe output signal IO is a signal to which folding modulation (signalfolding modulation) is applied. In this way, the ΔΣ modulation unit 82performs the folding modulation, and the dependency on past signals isreduced. Therefore, according to the reception circuit 61 of the presentembodiment, the edges can be more surely detected than in, for example,the reception circuit 61 described in the first embodiment. In addition,the edges can be more surely detected than in a ΔΣ modulation unit ofthe type that feeds back the comparison results of the comparisoncircuit 82 c in two values (+1, 0) to the subtraction circuit 82 a (thatis, ΔΣ modulation unit that performs ΣΔ modulation of 1 bit). This isbecause 0 or +1 is always fed back in the ΣΔ modulation of 1 bit, andonly signals with positive values can be handled. However, when thecomparison results of the comparison circuit 82 c are fed back in oddvalues, such as three values and five values, to the subtraction circuit82 a, no-signals in the state of 0 (midway between VTP0 and VTN0) canalso be handled in addition to the positive and negative signals.

Note that as mentioned here, the feedback to the subtraction circuit 82a can be performed in any odd values, and the values are not limited tothe three values illustrated in FIG. 14A or the five values illustratedin FIG. 14B. Note that when, for example, the feedback is handled in2m+1 values, the comparison circuit 82 c can include m comparatorscorresponding to positive values and m comparators corresponding tonegative values.

In addition, when the comparison results of the comparison circuit 82 care fed back in five values (+2, +1, 0, −1, and −2) to the subtractioncircuit 82 a as in the example illustrated in FIG. 16(c), the dependencyon past signals is smaller than in the case of the feedback in threevalues, and the edges can be more surely detected. In addition, thefolding modulation allows to use a continuous-time integrator to executesignal processing, and there is also an advantageous effect that theloss of signal can be smaller than in the process using the multi-valuedAD as disclosed in, for example, Non Patent Document 1.

The output signal CO of the analog circuit 71 is a pulse signal of threevalues including a plurality of pulses with respect to one chip of thechip sequence transmitted by the sensor controller 31 as describedabove. As illustrated in FIG. 16(d), the output signal CO is a signalincluding a pulse of +1 when the output signal IO is higher than thereference potential VTP and including a pulse of −1 when the referencesignal IO is lower than the reference potential VTN at the timing of thegeneration of each pulse.

As can be understood by comparing FIGS. 16(a) and 16(d), the outputsignal CO includes a large number of pulses other than the pulsescorresponding to the edges of the pulse signal transmitted by the sensorcontroller 31. Therefore, if the known pattern used in the firstembodiment (chip sequence obtained by applying Manchester coding to thespread code) is also used in the present embodiment, proper correlationoperation results may not be obtained. However, the known pattern usedin the present embodiment includes a chip sequence of three valuesincluding one chip with respect to one chip of the output signal CO, inwhich only one chip becomes “4” according to the change from “+1” to “0”in the transmission chip sequence, only one chip becomes “+1” accordingto the change from “0” to “+1” in the transmission chip sequence, andthe other chips are “0” as illustrated in FIG. 16(e). Therefore, even ifpulses other than the pulses corresponding to the edges of the pulsesignal are included in the output signal CO, this is not reflected onthe results of the correlation operation. Therefore, proper correlationoperation results can be obtained as illustrated in FIG. 16(f) based onthe output signal CO obtained as a result of the ΔΣ modulation.

As described above, according to the pen 2 of the present embodiment,the edges can be surely detected by the folding modulation executed bythe ΔΣ modulation unit even if there is dullness in the waveform of theuplink signal US, and this increases the possibility that the pen 2 candetect the edges. Therefore, the pen 2 can properly receive the uplinksignal US.

In addition, the digital circuit 72 performs the correlation operationusing three values of +1, 0, and −1, and therefore, proper correlationoperation results can be obtained based on the output signal CO obtainedas a result of the ΔΣ modulation.

Although the preferred embodiments of the present invention have beendescribed, the present invention is not limited to the embodiments inany way, and it is obvious that the present invention can be carried outin various modes without departing from the scope of the presentinvention.

For example, the first and second embodiments may be used incombination. That is, the sensor controller 31 that transmits the uplinksignal US so as to enhance the edges and the pen 2 that uses thecorrelation operation based on ΔΣ modulation and three values to receivethe uplink signal US can be used in combination. In this way, the pencan more properly receive the uplink signal US.

DESCRIPTION OF REFERENCE SYMBOLS

1: Position detection system

2: Pen

3: Tablet

3 a: Touch surface

20: Core

21: Pen tip electrode

23: Pen pressure detection sensor

24: Circuit board

25: Battery

30: Sensor electrode group

30X, 30Y: Sensor electrode

31: Sensor controller

32: Host processor

33: Charger

41: Logic unit

42: Transmission unit

43: Reception unit

44: Selection unit

50: Code sequence holding unit

51: Spread processing unit

51A: Signal source of pulse signal generated by spread processing unit51

52: Transmission processing unit

52A: Signal source of delay signal generated by transmission processingunit 52

54 x, 54 y: Switch

55 x, 55 y: Conductor selection circuit

60: Switch

61: Reception circuit

62: Controller

63: Transmission circuit

71: Analog circuit

72: Digital circuit

73: Pattern storage unit

74: Pulse density detection unit

80: High-pass filter

81: Amplification circuit

82: ΔΣ modulation unit

82 a: Subtraction circuit

82 b: Addition circuit

82 c: Comparison circuit

82 d, 82 e: Delay circuit

87: Edge matched filter

88: Uplink signal restoration unit

100: Output circuit

101: Potential generation circuit

ACa to ACd: AND circuit

C: Capacitance

C1, Ca to Cd: Capacitive element

CK1, CK2: Clock

cmd: Command

CO: Output signal of analog circuit 71

CPa to CPd: Comparator

DO: Output signal of amplification circuit 81

E1, E2: Edge

E3: Return edge

FO: Output signal of edge matched filter 87

IO: Output signal of addition circuit 82 b

OPa to OPd: Op amp

P: Preamble

R: Region

R1 to R8, Ra to Rk, Rm, Rn: Resistance element

Res: Response data

Rx: Reception signal

Sato Si: Switch

sTRx, sTRy, selX, selY: Control signal

T: Chip length of spread code

UN: Low frequency noise

US: Uplink signal

VDD: Higher power potential

VSS: Lower power potential

Vref, VTP, VTP0, VTN0, VTN: Reference potential

The invention claimed is:
 1. A pen that receives transmission datatransmitted through a sensor electrode group by a sensor controller thatdetects the pen, the pen comprising: a pen tip electrode arranged near apen tip; a differential circuit that detects edges of a signal led tothe pen tip electrode; a ΔΣ modulation unit that uses two referencepotentials corresponding to at least positive and negative values,respectively, to compare an output signal of the differential circuitand the two reference potentials and that executes feedback processingof comparison results; and a digital circuit that performs a correlationoperation of an output signal of the ΔΣ modulation unit and knownpatterns to detect the transmission data.
 2. The pen according to claim1, wherein the known patterns are chip sequences of three values.
 3. Thepen according to claim 2, wherein the ΔΣ modulation unit uses two ormore first comparators corresponding to positive values and two or moresecond comparators corresponding to negative values to execute foldingmodulation.
 4. The pen according to claim 3, wherein an output signal ofthe ΔΣ modulation unit is a pulse signal of three values, and thedigital circuit performs a correlation operation of the pulse signal ofthree values and the chip sequences of three values to detect thetransmission data.
 5. The pen according to claim 3, wherein an outputsignal of the ΔΣ modulation unit is a pulse signal of five values, andthe digital circuit performs a correlation operation of the pulse signalof five values and the chip sequences of three values to detect thetransmission data.
 6. The pen according to claim 1, wherein thedifferential circuit includes a variable gain amplification circuit, andthe pen further includes a control circuit that controls gain of theamplification circuit based on pulse density of the output signal of theΔΣ modulation unit.